During the last years, there has been an increasing demand for alcoholic beverages with reduced alcohol content, in particular beer and wine. At the same time the taste of these beverages should be maintained as far as possible so as not to be distinguishable from the taste of the beverages with the original alcohol content. Hereinafter the term low-alcohol beverages will be used for beverages with reduced alcohol content.
There are several reasons for the increased demand for low-alcohol beverages. First it is to be noted that the reduction of the alcohol content causes a reduction of the calorie content. This means that low-alcohol beverages can also be enjoyed by those people who are on diet for health reasons or who must not drink conventional alcoholic beverages for other reasons. Furthermore, the number of traffic accidents due to alcohol has led to an increase of traffic checks and punishments as well as to an increased awareness concerning the influence of alcohol on traffic. The danger due to alcohol can be reduced by low-alcohol beverages without substantially changing the drinking habits.
There have been quite some efforts to use the conventional processes for the separation of alcohol and ethanol, respectively, from its aqueous solutions and also for the reduction of the alcohol content of alcoholic beverages.
It is essential for the success of such a process that--apart from the desired reduction of the content of alcohol--no other changes occur in the beverage, in particular with respect to taste, appearance, and well keeping.
As a more volatile component, ethanol can be distilled off from alcoholic beverages, like wine or beer, so that the ethanol content of the beverage can be reduced. Such a process has been described, for example for beer, in Brauereiindustrie 71 (1986), page 480. The distillation must be carried out at low temperature and thus under reduced pressure to preserve the heat-sensitive constituents of the beer. Under these conditions, besides ethanol, other substances which are important for the taste, are removed depending on their volatility as well, so that a change in taste cannot be avoided. Furthermore, the required temperatures will cause a denaturation of the protein components leading to a change of taste and appearance of the low-alcohol beer as well. Further, the distillation under reduced pressure removes free carbon dioxide from the beer, which carbon dioxide must be recompressed and recycled. The technical equipment required and the costs for such a vacuum distillation are high without eventually yielding a satisfactory result.
Another process for the reduction of the content of alcohol in alcoholic beverages is described in Weinwirtschaft, Tech. 9 (1986), page 346. In a dialysis process the liquid, the alcohol content of which is to be reduced, is fed across one side of a porous dialysis membrane, while an alcohol-absorbing liquid, for example water, flows at the other side of the membrane. Alcohol diffuses from the alcoholic phase, for example wine, into the absorbing liquid according to the concentration difference. However, because for all components of the wine there exists a corresponding concentration difference across the membrane, these components diffuse along with the alcohol, so that such a process causes a loss of taste substances as well. A further disadvantage resides in that the absorbing liquid (dialysate) is obtained with a very low alcohol content and can hardly be commercially used or disposed of.
Another process for alcohol reduction is described in U.S. Pat. No. 4,617,127 and EP-A-0 162 240 taking advantage of the fact that membranes for reverse osmosis having a salt retention capacity, for example for sodium chloride, of more than 97%, have a retention capacity for ethanol of less than 90%. If beer or wine having an alcohol content of 4% or 10%, respectively, is subjected to the process of reverse osmosis, a permeate is obtained on the one hand consisting essentially of water and some alcohol, as well as a retained material (retentate) on the other hand having a higher alcohol concentration than the original beverage. A product having an alcohol content less than the alcohol content of the original beverage is obtained if the retentate is rediluted with pure water to the original volume. Disadvantages with this process are also, that under the influence of the high pressure required a denaturation of taste substances occurs and that, besides alcohol and water, other taste substances permeate through the membrane thus being lost. Further, an alcoholic solution of low concentration is obtained as permeate, which must be processed or disposed of. Despite all these disadvantages this process of reverse osmosis is used in large scale operation emphasizing the need for a better process.
These problems lead directly to the object of the invention, the solution of which is defined in claim 1.